In order to expect Ordovician limestone dewatering quantity, Q-S curve method was adopted. Q-S curve was mapped based on dewatering experiment, empirical equation type was settled based on the shape of the curve, the coefficient of empirical formula was calculated by least square method, empirical formula was set up, dewatering depth of drainage hole was calculated when water bursting coefficient reduced to 0.06 MPa/m, Ordovician limestone dewatering quantity was got based on dewatering depth in the formula. The expected dewatering quantity subtracts existed Ordovician limestone dewatering quantity influencing radius, which is the dewatering quantity of safe mining. The technology avoids the error in calculating hydrogeological parameter, with easy conduction.